Where do the switches on the left go -- are they margin switches for the power?
Looks to be of Negibus vintage, but who knows if it's even PDP-8. Could be PDP-15 or something.
I have a (similar sized small backplane) TC02 (or was it TC04?) backplane somewhere that basically was intended to write half inch magtape TD8E style, in a very inefficient format. (Basically, one word tape blocks.) Maybe this is something like that, but earlier?
I assume there aren't any surviving modules or markings on the other side.
That toggle switch on the pin side about 6 cards from the left is a pretty distinctive thing. It does look to use single sided connector blocks which probably makes it a negibus backplane. It doesn't look like anything in my Straight 8. Could it be a formatter for one of the drum units or maybe the DF-32 or RF08?
Here is where having all the documentation searchable would probably help.
With the four switches it looks very similar to the DEC A-D Converter backplane. The same backplane (obviously wired differently) seems to have been used in the PDP-9 LT09A, ME09 and other units.
Yes, an unwired backplane can be used for many different purposes depending on wiring. I think the OP want to know based on how this one is wired what it was for.
Yes I realise that. Vince's comment about being PDP-8 or PDP-15 - whether this backplane was used for them I can't answer, but was just pointing out that that backplane was definitely used for PDP-9 peripherals. I have the AD Converter (used for PDP-8 and PDP-9) and I checked the print sets I have for those other peripherals. 'MTC' sounds like it could be Magnetic Tape Controller.
I am sure DEC used that basic backplane for many systems. Why not. Saves $$ in design costs have separate ones for each. Still would be interesting to see what it was for. I don't ever remember seeing a switch on the wiring side like that on any backplanes I have seen.